This invention relates generally to the selective separation of particles of metal from a mixture of particles, and more specifically relates to the selective separation of fine metal particles from a mixture of fine particles of metal and sand, clay and the like, by injecting the fine particle mixture against a mercury media, so that the metal particles heavier than the media penetrate the media and the other particles lighter than the media are rejected by the media. Still more specifically, the invention relates to a particle separator utilizing a centrifugal force to increase the weight and shorten the "fall time" of particles and thereby cause metal particles of a mixture having a greater specific gravity than a media substance, to contact, and penetrate the media.
As is well known, numerous devices and methods have been used heretofore for separating precious metal particles, such as gold particles from particles of sand, clay and the like. The various methods commonly used are sluicing, leaching, and amalgamation and were generally successful for extracting precious metal particles larger than one millimeter.
It is believed that there is a vast supply of various kinds of metals in nature in the form of fine particles and microfine particles (less than 60 microns in size). Slucing techniques have heretofore been tried to extract such fine particles of metal and recovery has been minimal and therefore unprofitable. This is attributed in part to the unpredictability of the rate of descent ("settlement or fall time rate") of the fine metallic particles through water. Moreover, when the metal particles are less than 60 microns, the surface area of the particles become exceedingly more important. The greater the flatness of the particles as compared to a spherical particle (minimum surface area) the rate of descent through the liquid is further decreased. (The flatness factor of a particle has been defined as the sum of the particle length and width divided by twice the thickness.) The greater the particle flatness, the greater the surface area of the particle, and the more frictional drag developes upon descent or movement through liquid, to impede movement. Therefore, to realize any fine metal particle recovery with the sluicing method, the water velocities must be delicately controlled.
Amalgamation processes have also been previously employed for extracting fine metal particles. Amalgamation separation requires a clean surface for the wetting and contact of the metal particles with a mercury surface, causing the metal particles to cling to the mercury surface and later to be separated from the mercury by any conventional means (such as electrolysis or distillation). Fine metal particles, however, do not readiy penetrate the mercury surface. This may be attributed to a thin water film collecting on the surface of the mercury which creates a barrier between the mercury and the particles trying to penetrate. Penetration by the fine metal particles is further inhibited by the flatness factor of the particles. When the surface area of the fine metal particles is greater, the penetrating capability of such particles is reduced particularly for overcoming any surface film.
U.S. Pat. No. 1,452,181, BUTLER (1923) entitled "Centrifugal Amalgamator" discloses a device in which material comprising ground ore and sand, water and mercury are injected therein and then subjected to a centrifugal force. The metal particles become separated from the ores and sand and brought into contact with successive amalgamated surfaces and the mercury inserted in the device, as the material is tumbled through the device. The metal particles having an affinity for mercury surfaces cling thereto. The mercury material is discharged from the device and the metal particles later collected, and the metal particles on the amalgamated surfaces are removed. BUTLER uses the centrifugal force to separate the metal particles from the sand so that the metal particles could come into contact with the amalgamated surfaces and the surfaces of the mercury inserted into the device which fill up successive troughs.
The invention herein utilizes the centrifugal force to initially build up a wall of a media such as mercury, and thereafter to propel a mixture of fine metal particles and particles of sand and the like against the media wall, so that heavier metal particles as compared with the mercury, contact penetrate and pass through the media and other particles lighter than the mercury, are blocked from entry into the media and discharged from the device.
A primary object of this invention is to provide a process for selectively separating fine metal particles from particles of sand, clay and the like.
Another primary object of this invention is to provide a mechanical process that selectively separates micron and submicron size particles that have a greater specific gravity than a media such as mercury and simultaneously to reject particles having a lighter specific gravity than the mercury.
Another object is to provide a process utilizing a centrifugal force to initially build up a wall of a media such as mercury and thereafter to impinge the media wall with a mixture including particles of metal, sand, clay and the like, causing selected metal particles to contact and penetrate the media and the other particles to be rejected by the media.
Another object is to provide a process for extracting fine metal particles from a mixture of particles by utilizing a media substance having a specific gravity less than the fine metal particles desired to penetrate and pass through the media but a greater specific gravity than the particles to be rejected by the media.
Another object is to selectively separate fine metal particles from particles of sand, clay and the like, by causing the fine metal particles to penetrate and pass through a media and build up a layer of the fine metal particles.
Still another object of the invention is to provide a method for the selective separation of particles of micron or smaller size including micron size particles of gold, platinum, and other metals which have a greater specific gravity than mercury.
Still another object is to utilize a centrifugal force to construct a wall of mercury around the inside surface of a rotating bowl; thereafter to propel a mixture including fine particles of metal and sand, clay and the like against the wall of mercury whereby fine metal particles having a specific gravity greater than the mercury, contact, penetrate and pass through the media wall to develope a layer of the fine metal particles between the inside surface of the bowl and the mercury wall.
Another object is to provide a selective separator device including a bowl having a plurality of scalloped compartments to receive a media substance through which fine metal particles having a specific gravity greater than the media penetrate and particles having a specific gravity less than the media are rejected.
Another object is to terminate the outer ends of the scalloped compartment with a cap to confine the mercury media in the compartment as the bowl is rotated for providing a centrifugal force.